1. Field of the Invention
The present invention relates to ring laser gyroscopes, and more particularly, to improvements in the structure of gas laser gyroscopes reducing gas flows therein.
2. Description of the Prior Art
The use of ring laser gyroscopes as guidance instruments has been known in the past. Typically, such lasers take the form of a closed resonator loop in which oppositely injected laser beams are bent into closed paths by various turning mirrors. Any rotation about an axis orthogonal to the plane of the loop then results in opposite frequency shifts of the two beams and the resulting beat frequency then provides a quantitative measure of the turning rate.
In this general arrangement the laser beams are typically turned by mirrors at the end of straight segments, one or more of which providing the location for the laser gain tube or the gain medium. Thus, the geometry of the ring laser gyroscope typically includes straight line segments of a resonator tube through which the beams are passed.
While the recent past has seen suggestions of solid state lasers for ring gyroscope use, the practicalities still dictate the use of gas lasers with substantial preference still remaining for the He-Ne (helium/neon) laser. Gas lasers, however, exhibit induced flows generally described by the work of I. Langmuir (1923) J. Franklin Institute 196,751 which are partly explained in terms of light velocity changes in a moving refractive medium, i.e., the Fresnel-Fizeau drag effect. Additionally, Doppler shifts are associated with the flow which, again, affect the frequency of the laser. This induced velocity change, therefore, inserts substantial null errors into the ring laser which, heretofore, has been carried as a readout bias. Any drifts, however, in this Langmuir flow present large potential for gyroscope errors and substantial research has been expended at reducing this induced flow.
Typical of these efforts are the teachings of U.S. Pat. No. 4,284,329 to Smith et al in which a partial restriction is inserted into the flow path. Alternatively, an opposite, compensating discharge path is provided, as in U.S. Pat. No. 4,397,027 to Zampiello et al. Each of these solutions, while suitable for their purposes, depend on cancellation or restriction of substantial gas flows and thus entail manipulations of large volumes which, in themselves, are prone to generate large errors. Thus, the prevailing practices in the past require close control at restricting or compensating large effects and consequently demand extreme accuracy in the implementation thereof.
Accordingly, techniques which directly address the phenomenon of gas flow are desired and it is one such technique that is disclosed herein.